I think Rory/Rorie is so cute for a little girl, but I probably wouldn't use it myself as Rory is pretty much only used on boys here. I also like Aura.
My idea is to skip the nn and just address her by her full name... I suppose if her mn starts w/ a J, she could be AJ, but I think Aurora should be left as is and not adulterated w/ a nn.
The only nn's I like for Aurora are Ora, Ori and maybe Ari (that's a stretch though). However, I don't think Aurora needs a nn to be honest. It's short enough. I love it, I think it's stunning, a nn is unnecessary
I had a dog named Aurora once, and we called her Rora. A girl at my school is named Aurora and sister calls her Ace. I also like Aura. Auri, Rory, Auror (:P), Ara, Ora, and Ro could be some others.